1. Field of the Invention
The present invention relates in general to a liquid crystal display (LCD) device and, more particularly, to a method and apparatus for testing an LCD device to detect a defective location on the LCD device precisely and rapidly without requiring a jig.
2. Description of the Related Art
Display apparatuses have become important as visual information transferring media. Among the display apparatuses, a cathode ray tube is widely used at present, but is disadvantageous in that its weight and volume are large. Therefore, various types of flat display apparatuses have been developed that are capable of overcoming the defects of the cathode ray tube. An LCD, a field emission display (FED), a plasma display panel (PDP), and an electroluminescence (EL) display are different examples of flat display apparatus. Most of these apparatuses are available in the market.
The LCD device is easily adaptive due its smallness which improves productivity. Thus, it is quickly replacing the cathode ray tubes in many applications. In particular, the LCD device of an active matrix type for driving a liquid crystal cell by using a thin film transistor (hereinafter referred to as “TFT”) has an advantage in that the picture quality it provides is excellent, and its power consumption is low. Such LCDs have been rapidly developed into a large size and high definition due to the recent productivity technology and research.
As shown in FIG. 1, in the LCD of the active matrix type, a color filter substrate 22 and a TFT array substrate 23 are assembled with a liquid crystal layer 15 therebetween. The LCD shown in FIG. 1 represents a portion of a total effective display.
The color filter substrate 22 includes an upper glass substrate 12, and a color filter 13 and a common electrode 14 formed thereon. Attached on a front surface of the upper glass substrate 12 is a polarization plate 11. In the color filter 13, the color filter layers of red, green and blue colors are disposed and transmit a light of special wavelength bandwidth to display a color. A black matrix (not shown) is formed between the color filters 13 of the adjacent color.
Data lines 19 and gate lines 18 cross each other on the entire surface of a lower glass substrate 16 in the TFT array substrate 23. TFTs 20 are formed at the intersections of the gate and data lines 18 and 19. A pixel electrode 21 is formed at a cell region between each of the data lines 19 and gate lines 18 on the entire surface of the lower glass substrate 16. Each TFT 20 switches a data transfer path between the corresponding data line 19 and the corresponding pixel electrode 21 in response to a scanning signal from the corresponding gate line 18 and thus drives the corresponding pixel electrode 21. A polarization plate 17 is installed on a rear surface of the TFT array substrate 23.
The liquid crystal layer 15 adjusts a transmitting quantity of an incident light via the TFT array substrate 23 in response to an electric field applied thereto. The polarization plates 11 and 17 installed on the color filter substrate 22 and the TFT array substrate 23 transmit the light polarized to one direction. When the liquid crystal layer 15 is at 90°TN mode, the polarization directions of the polarization plates 11 and 17 vertically cross each other. An alignment film (not shown) is formed on the facing surfaces of the color filter substrate 22 and the TFT array substrate 23.
A process for fabricating the LCD device of the active matrix type is divided into a substrate cleaning, a substrate patterning, an alignment forming/rubbing, a substrate assembling/a liquid crystal material injecting, a mounting, an inspecting and a repairing.
Generally, impurities on the substrate surface of the LCD device are removed by a detergent in the substrate cleaning process. The substrate patterning process is divided into a patterning process of the color filer substrate and a patterning process of the TFT array substrate. The alignment film forming/rubbing process involves applying an alignment film to each of the color filter substrate and the TFT array substrate and rubbing the alignment film. The substrate assembling/liquid crystal injecting process is to assemble the color filter substrate and the TFT array substrate by using a sealant, to inject the liquid crystal and a spacer through a liquid crystal injection hole and then to seal the liquid crystal injection hole.
In the mounting process of the liquid crystal panel, a tape carrier package (hereinafter referred to as “TCP”) is connected to a pad part on the substrate, wherein the TCP has integrated circuits mounted thereon such as a gate drive integrated circuit and a data drive integrated circuit. Such drive integrated circuits may be directly mounted on the substrate by using a chip on glass (hereinafter referred to as “COG”) method besides a TAB (Tape Automated Bonding) using the TCP described above.
The inspecting process includes a first electrical inspection performed after forming a variety of signal wirings such as the data line and the gate line on the TFT array substrate and the pixel electrode, and a second electrical inspection and a visual inspection performed after the substrate assembly/liquid crystal injection process. Specifically, the electrical inspection of the signal wirings of the TFT array substrate and the pixel electrode of the lower substrate performed before the substrate assembling process may reduce an undesirable ratio and a waste matter and may find a defective substrate capable of repairing at an early stage.
The repairing process performs a restoration for a repairable substrate determined by the inspecting process. However, in the inspecting process, defective substrates beyond repair are discarded.
The device as shown in FIG. 2 may be used in an inspection process carried out before the substrate assembling. The inspection device shown in FIG. 2 is fully described in U.S. Pat. No. 5,377,030.
Referring to FIG. 2, the inspection device of the related art includes an inspection switch device 34 for selectively supplying a voltage from an inspection power supply 36 to a video signal input wiring, and a voltage from a current-voltage amplifier 38 under the control of a driving signal generation unit 35, a scanning switch device 30 for supplying the inspection voltage from the video signal input wiring 32 to the data lines 28 of a TFT array 46 of an active matrix LCD under control of an H scanning circuit 24, a V scanning circuit 42 for driving the gate lines 26 of the TFT array 46 under control of the driving signal generation unit 35, and a determining unit 40 for determining an electrical defect in the TFT array 46. The data lines 28 and gate lines 26 cross each other in the TFT array 46, and TFTs are formed at their intersections. Further, common wirings 33 and a storage capacitor Cst between the common wirings 33 and a drain electrode of the TFT are formed in the TFT array 46.
The inspection of the TFT array 46 includes a sequence of loading a substrate having the TFT array 46 formed thereon to the inspection device, writing the inspection voltage to the TFT array 46 and reading a signal from the TFT array 46.
After loading the substrate having the TFT array 46 to the inspection device, the writing process of the inspection voltage is performed. In the writing process of the inspection voltage, the inspection switch device 34 is connected to the first terminal 34a and the scanning switch device 30 is turned on under control of the H scanning circuit 24. Accordingly, the inspection voltage generated from the inspection power supply 36 is supplied to the data lines 28 of the TFT array 46 via the inspection switch device 34, the video signal input wiring 32 and the scanning switch device 30. At the same time, the V scanning circuit 42 supplies a test scan voltage to the gate lines 26 under control of the driving signal generation unit 35. Then the TFTs are turned on in the selected lines of the TFT array 46, and the inspection voltage on the data lines 28 is charged to the storage capacitors Cst via the TFTs.
In the reading process of the inspection voltage, the inspection switch device 34 is connected to the second terminal 34b and the scanning switch device 30 is turned on under control of the H scanning circuit 24. At the same time, the V scanning circuit 42 supplies the test scan voltage to the gate lines 26 under control of the driving signal generation unit 35. Then, the TFTs are turned on in the selected lines of the TFT array and the voltage of the corresponding storage capacitor Cst is supplied to the current-voltage amplifier 38 via the TFTs, the data line 28, the scanning switch device 30, the video signal input wiring 32 and the inspection switch device 34. The voltage read from the storage capacitor Cst is supplied to the determining unit 40 after being amplified by the current-voltage amplifier 38, and the determining unit 40 determines if there is a defect in the TFT array 46 based on the voltage supplied by the current-voltage amplifier 38.
However, since the substrate (having the TFT array 46) to be inspected is not equipped with the driving circuit and the inspection device, a separate jig is needed to accommodate the driving signal generation unit 35, the H scan circuit 24, the V scan circuit 42, the scanning switch device 30, the video signal input wiring 32, the inspection switch device 34, the inspection power supply 36, the current-voltage amplifier 38 and the determining unit 40. As a result, there is a problem that the inspection device of the related art shown in FIG. 2 needs a high price jig. Further, if the resolution of the LCD or a model is changed, the jig needs to be changed correspondingly. On the other hand, if the TFT array 46 is inspected by a block dividing method concurrently driving a plurality of gate lines 26 and a plurality of data lines 28, the number of input/output terminals of the jig and the circuit price of the jig may be reduced. However, there is another problem that a defect location within the block cannot be detected with precision.